1. Field of the Invention
The present invention relates to a display device lighting unit, a lamp holder and a liquid crystal display device. More particularly, it relates to a display device lighting unit and a lamp holding system therefor, which are suited for use in constituting a backlight for a liquid crystal display device of the transmission or semitransmission type having a transmission region in the liquid crystal display element and to a liquid crystal display device equipped with the display device lighting unit.
2. Prior Art
A display device lighting unit illuminates a device having light-based display means and is widely used in the backlight section of a liquid crystal display device, for instance. Thus, the liquid crystal panel itself in a liquid crystal display device does not emit light and, therefore, a liquid crystal display device of the transmission or semitransmission type generally has a display device lighting unit as a backlight section for giving light to the liquid crystal panel. Such a liquid crystal display device is indispensable for information or video display means and, in recent years, high quality products in which the characteristics of liquid crystal displays, namely their being low in electricity consumption, light in weight and thin, are made use of have attracted attention and the field of their application has become widened in display panels of household video monitors, monitors for industrial machines and tools, portable information terminals and so forth.
Meanwhile, the backlight for use in a liquid crystal display device currently includes two main types, namely the edge light type (side light type) and the just-under-panel type (direct type). A structural feature of the edge light type is that a rod-shaped light source 102, such as a cold cathode fluorescent tube, is disposed on the side of a transparent plate 101 called a light guide plate, as shown in FIG. 10. In this case, light enters the light guide plate 101 from the light source and exits from inside the light guide plate 101 toward the liquid crystal panel 105 by frosting, printing, prismatic and the like. Whereas the resulting module can be made thin in this manner, an increase in light source as made in an attempt to increase the brightness directly influences the thickness of the module. Further, a heavy continuous body made of an acrylic, for instance, is used as the so-called light guide plate 101 and, therefore, when the size is large and exceeds 20 inches, its weight is very heavy.
On the other hand, it is a structural feature of the direct type that a display device 117, such as a liquid crystal panel, is provided, at the back thereof, with a plurality of rod-shaped light sources 113, such as cold cathode fluorescent tubes, as shown in FIG. 11. In this case, the light from the rod-shaped light sources 113 almost directly enters the display element 117, and a diffuser 115 for diffusing the light from the rod-shaped light sources uniformly over the screen and an optical sheet 116 comprising a diffusing sheet, a condensing lens, a light polarization selective reflecting/transmitting sheet and a protective/diffusing sheet, among others, are disposed and, then, the display element 117 is disposed. This constitution has the following advantages: a large number of light sources 113 can be disposed and the quantity of light can be increased, the loss of light is small owing to the direct incidence of light on the display element 117, and large displays exceeding 20 inches can be realized with ease. On the other hand, the number of light sources 113 is great and the number of relevant parts becomes increased, and the driving circuit for the light source 113 becomes a large-scaled one. Furthermore, the electricity consumption increases, and the total heat generation becomes increased.
The progress of such liquid crystal display devices began with small-sized display elements, and the market therefor has been broadened to displays for notebook personal computers (PCs) and cellular phones with the development of the relevant technologies. In these fields, the main display size is up to about 15 inches and it is a necessary condition that the devices be thin. Thus, from the commercial value viewpoint, the edge light system has been employed in those fields.
At present, liquid crystal display devices are getting larger and larger as a result of completion of a process using larger mother glass sheets, among others, and now occupy a good position among household televisions (20-inch to 50-inch). For such televisions, brightness is one of the important performance characteristics as compared with PCs and cellular phones. For example, the specification value of brightness for PC monitors is generally about 250 candelas (cd/m2), whereas the brightness specification for televisions as currently required is at least 500 candelas (cd/m2). In view of such background, the direct backlight system is appropriate for providing large-sized and high-brightness backlights.
Regarding lighting units for display devices which can be applied to the conventional liquid display devise, there have been disclosed a lamp holder made of a flexible transparent material and having the shape of an arc holder with a partial opening (cf. e.g. Japanese Kokai Publication 2001-210126, pages 1-2), a backlight device in which the reflector for condensing the light emitted from a light source to the light guide plate is made of a metal and is supporting the light source (cf. e.g. Japanese Kokai Publication H10-207406, pages 1-2), and a fluorescent lamp unit in which a fluorescent lamp is contained in the inside of a gutter-shaped unit holder and, between the fluorescent lamp and unit holder, there is disposed a lamp holder made of a light-transmitting or light-reflecting synthetic resin (cf. e.g. Japanese Kokai Publication H09-330613, pages 1-2).
However, there is still room for contrivance for adapting these devices to the field of liquid crystal displays, among others, where higher quality and larger sizes are required for improving the commercial value thereof and at the same time reductions in cost are required. For example, in developing liquid crystal television sets, in particular, there is room for contrivance for improving the characteristics thereof by bringing advantages, from the production viewpoint, by reducing the number of parts, and by enabling reductions in dispersion of display quality by decreasing the deviations in assemblage in the process of producing lighting devices or units, or attaining higher levels of quality and commercial value by preventing the display quality from lowering due to the structure of lighting devices.
Further, a lighting device has been disclosed in which a plurality of fluorescent lamps are commonly connected at one external electrode side and at the other external electrode side, respectively, and the whole is connected to one booster lighting circuit to thereby stabilize the fluorescent lamps (cf. e.g. Japanese Kokai Publication 2003-36723, pages 1-2). In this lighting device, a plurality of fluorescent lamps are connected to one lighting circuit by means of a lamp fixer made of a conductive metal and having a plurality of grooves having the shape of a U in section. With respect to such a device, however, there is room for contrivance for providing a product showing higher display performance characteristics for application thereof to a liquid crystal television and the like which requires a large size and high-brightness backlight or in cases where the lamp fixing portions are made of a rubber or plastic.
Meanwhile, there is disclosed a lighting device equipped with a pair of supporting mechanisms for supporting a bent type discharge lamp between casing side wall portions in a sandwiching and fitting manner (cf. e.g. Japanese Kokai Publication H07-72476, pages 1-2). In this lighting device, one bent portion of the lamp is supported at one site. With devices of this kind, however, deviations may result in the step of mounting lamps and such deviations may influence the display quality or reliability. In the case of large-sized, high-brightness lighting devices, in particular, it is important to decrease such deviations in mounting lamps. Therefore, in such a prior art lighting device, there is room for contrivance for improving the shape of the supporting member by which the bent portion of a lamp is to be fixed.